Semiconductor devices are found in many products in the fields of entertainment, communications, networks, computers, and household markets. Semiconductor devices are also found in military, aviation, automotive, industrial controllers, and office equipment. The semiconductor devices perform a variety of electrical functions necessary for each of these applications.
The manufacture of semiconductor devices involves formation of a wafer having a plurality of die. Each semiconductor die contains hundreds or thousands of transistors and other active and passive devices performing a variety of electrical functions. For a given wafer, each die from the wafer typically performs the same electrical function. Front-end manufacturing generally refers to formation of the semiconductor devices on the wafer. The finished wafer has an active side containing the transistors and other active and passive components. Back-end manufacturing refers to cutting or singulating the finished wafer into the individual die and then packaging the die for structural support and environmental isolation.
One goal of semiconductor manufacturing is to produce a package suitable for faster, reliable, smaller, and higher-density integrated circuits (IC) at lower cost. Flip chip packages or wafer level chip scale packages (WLCSP) are ideally suited for ICs demanding high speed, high density, and greater pin count. Flip chip style packaging involves mounting the active side of the die facedown toward a chip carrier substrate or printed circuit board (PCB). The electrical and mechanical interconnect between the active devices on the die and conduction tracks on the carrier substrate is achieved through a solder bump structure comprising a large number of conductive solder bumps or balls. The solder bumps are formed by a reflow process applied to solder material deposited on contact pads which are disposed on the semiconductor substrate. The solder bumps are then soldered to the carrier substrate. The flip chip semiconductor package provides a short electrical conduction path from the active devices on the die to the carrier substrate in order to reduce signal propagation, lower capacitance, and achieve overall better circuit performance.
Some applications utilize large solder bumps, while other applications require thin wafers to reduce die and package thickness. The thin wafers are made by backgrinding conventional wafers to the desired thickness. The wafer backgrind is typically done before the solder bumps are formed. In applications requiring both large solder bumps and thin wafers, wafer warpage or breakage is a recurring design issue in view of the bump height variation and stress of reflowing the large solder bumps on the thin wafer, as well as using known front-side support structures during backgrinding. One known approach uses a thick tape covering the active surface of the wafer after solder bump attachment for the front-side structural support during backgrinding. However, the tape is costly to use and adds manufacturing steps to apply and remove. The removal of the front-side tape, typically by mechanical peel prior to flip chip attachment, may break a thin wafer.
A need exists to form large solder bumps on thin wafers without causing wafer warpage or breakage.